1. Field of the Invention
The present invention relates to a vehicle engine and particularly to an intake device in the vehicle engine having an injector injecting fuel (e.g. gasoline) into an intake pipe.
2. Related Art
A four-stroke-cycle gasoline engine includes a crank case in which a crankshaft is rotatably supported and a cylinder provided in the crank case. A piston, which is accommodated and reciprocates in the cylinder, is connected to the crankshaft through a connecting rod. A combustion chamber defined over the top of the piston by the cylinder and a cylinder head provided over the cylinder. An intake pipe supplying the combustion chamber with air-fuel mixture and an exhaust pipe discharging combustion gases are connected to the cylinder head. An intake port opened to the combustion chamber is connected to the intake pipe and an exhaust port also opened to the combustion chamber is connected to the exhaust pipe. The cylinder head includes an intake valve and exhaust valve, which open or close the intake port and exhaust port, respectively.
When the air-fuel mixture enters the combustion chamber through the intake port, the air-fuel mixture may swirl, thereby combustion is completed in a relatively short period of time. According to JP-A-2002-317639, the air-fuel mixture swirls in the combustion chamber by changing the open-close lift amount and valve-opening timings between two intake valves which open or close corresponding intake ports in a cylinder head, respectively.
In order to generate swirl in a combustion chamber as described above procedure, it is required to change open-close lift amount and valve-opening timings between two valves, respectively, therefore, complex valve-operating mechanism is required, which results in high manufacturing cost.
There are transverse-mounted type and longitudinal-mounted type engines in typical engines for vehicles including an all terrain vehicle. In the transverse-mounted engine in which a crankshaft is transversely mounted in a vehicle along the vehicle width, an intake port is located in a front side of the engine in a vehicle driving direction (vehicle longitudinal direction), and an exhaust port is located in a rear side of the engine in the vehicle driving direction. In this configuration, since the intake port is positioned at the front of the vehicle, wind based on a vehicle speed enters the engine from an air intake disposed at a front side of the engine. Therefore, fresh air is efficiently supplied into the engine. On the other hand, in the longitudinal-mounted type engine, the engine is mounted in the vehicle such that the crankshaft is parallel to the vehicle driving direction, thus the intake and exhaust ports are located left or right side of a cylinder head, respectively.
In the cylinder head, a valve-operating mechanism including a cam shaft operating a valve-operating cam and a rocker shaft supporting a rocker arm is accommodated in a space defined by the cylinder head and a rocker cover combined with it. The cam shaft has a driven sprocket driven through a chain meshed with a driving sprocket fitted to the crankshaft. In an engine to be mounted in the vehicle in longitudinal direction (vehicle traveling direction) thereof, the driven sprocket projects out over the intake port or the exhaust port in an upper side of the cylinder head. Therefore, in order to supply the fresh air to the intake port from the air intake disposed on the front side of the engine, the intake pipe is required to climb over a portion of the rocker cover where the driven sprocket is accommodated and to go around an upper portion of the engine. Accordingly, a height of the engine including the intake pipe increases. Moreover, when an injector for injecting gasoline into the intake pipe is mounted on the intake pipe, the height of the engine including the injector further increases.